I'm not really sure why you want to switch. Are the teeth not progressing as the Invisalign Clin-Chek predicted? You might just need a mid-course correction. Are you not wearing the aligners at least 22-hours daily?
Costs vary by region and specialists. I would imagine the orthodontist...
The boil and bite mouthguard will not hold teeth well as it is too soft and will not fit anywhere near as well as a custom made retainer. Please return to your dentist and have a temporary retainer and a new retainer made. They can probably get you a temporary in a day or two...
Actually she is using invisalign (Invisalign Teen) has a blue dot to indicate compliance. It does not matter to be honest. As long as you have been wearing the recommend timeframe I would change and make sure they fit correctly. If they do, then switch, if not call your dentist